trace: Trace bdrv_aio_flush()

Add a trace event for bdrv_aio_flush() to complement the existing
bdrv_aio_readv() and bdrv_aio_writev() events.
Signed-off-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>

block.c

@@ -2477,6 +2477,8 @@ BlockDriverAIOCB *bdrv_aio_flush(BlockDriverState *bs,
 {
     BlockDriver *drv = bs->drv;
 
+    trace_bdrv_aio_flush(bs, opaque);
+
     if (bs->open_flags & BDRV_O_NO_FLUSH) {
         return bdrv_aio_noop_em(bs, cb, opaque);
     }

trace-events

@@ -51,6 +51,7 @@ disable multiwrite_cb(void *mcb, int ret) "mcb %p ret %d"
 disable bdrv_aio_multiwrite(void *mcb, int num_callbacks, int num_reqs) "mcb %p num_callbacks %d num_reqs %d"
 disable bdrv_aio_multiwrite_earlyfail(void *mcb) "mcb %p"
 disable bdrv_aio_multiwrite_latefail(void *mcb, int i) "mcb %p i %d"
+disable bdrv_aio_flush(void *bs, void *opaque) "bs %p opaque %p"
 disable bdrv_aio_readv(void *bs, int64_t sector_num, int nb_sectors, void *opaque) "bs %p sector_num %"PRId64" nb_sectors %d opaque %p"
 disable bdrv_aio_writev(void *bs, int64_t sector_num, int nb_sectors, void *opaque) "bs %p sector_num %"PRId64" nb_sectors %d opaque %p"